The invention relates to a semi-spherical shoe and more particularly, to a semi-spherical shoe which is preferred to be interposed between a piston of a swash plate compressor and a swash plate.
The use of the semi-spherical shoe in a swash plate compressor which is provided with a semi-spherical surface and a flat end face is known in the art.
In the prior art practice, the entire semi-spherical surface of the semi-spherical shoe has been formed substantially to a uniform surface roughness. The semi-spherical shoe has its semi-spherical surface fitted into a semi-spherical recess formed in the piston and thus is disposed in sliding contact therewith. However, the entire semi-spherical surface is not disposed in sliding contact with the semi-spherical recess in the piston, but it is known that an annular region which is disposed toward the axial center of the semi-spherical shoe is disposed in sliding contact with the semi-spherical recess. Thus, the semi-spherical surface of the semi-spherical shoe includes a sliding contact region which is disposed in sliding contact with the semi-spherical recess in the piston, and a non-sliding contact region which is not disposed in sliding contact with the semi-spherical recess in the piston as is known in the art.
In the conventional semi-spherical shoe, the entire semi-spherical surface, thus, both the sliding contact region and the non-sliding contact region are formed to the same surface roughness. However, it is found by a study of a conventional semi-spherical shoe by the present inventor that a fine roughness of the semi-spherical surface has been effective in view of the sliding response. On the contrary, when the surface roughness of the semi-spherical surface is fine, the semi-spherical surface repels a lubricant oil, and thus there results a disadvantage that the lubricant oil is less susceptible to be guided toward the sliding contact region.
In view of the foregoing, the present invention provides a semi-spherical shoe including a semi-spherical surface which is fitted into a semi-spherical recess formed in one of members and an end face which is disposed in sliding contact with a flat surface formed on another member, in which a non-sliding contact region of the semi-spherical surface which is not disposed in sliding contact with the semi-spherical recess has a roughness which is greater than the roughness of a sliding contact region of the semi-spherical surface which is disposed in sliding contact with the semi-spherical recess.
With this arrangement, the greater surface roughness of the non-sliding contact region area than the surface roughness of the sliding contact region of the semi-spherical surface prevents a lubricant oil from being repelled by the non-sliding contact region, and allows the lubricant oil to be smoothly supplied to the sliding contact region through the non-sliding contact region. Because the sliding contact region has a fine surface roughness, there is provided a semi-spherical shoe which exhibits an excellent sliding response.